Ethanol is frequently co-abused with other drugs, therefore studies examining self-administration of ethanol in combination with other drugs may help develop animal models which can assess the efficacy of behavioral and pharmacological treatments designed to reduce ethanol drinking in polydrug abusers. This proposal is comprised of three related studies. Each study is designed to asses an individual aspect of the reinforcing effects of ethanol alone as well as ethanol combined with another drug of abuse. In the first study rats will be trained to orally self-administer a combination of ethanol and pentobarbital after which the reinforcing properties of ethanol and the drug mixture will be assessed. This will be accomplished by examining the relative reinforcing effects of a number of ethanol/pentobarbital combinations compared to ethanol alone using concurrent self-administration procedures over a range of fixed-ratio values. The second study in the series proposes to examine the effects of naltrexone on self-administration of ethanol and an ethanol plus pentobarbital mixture. This study will use a novel multiple schedule of ethanol and ethanol plus pentobarbital self-administration to sequentially assess the effects of naltrexone on responding for both ethanol and the mixture within a single test session. The third study will use an ethanol fading procedure to attempt to train rats to orally self-administer pentobarbital. If successful, this training procedure may prove effective at inducing rats to orally self-administer other drugs of abuse as well. It is hoped that these studies will produce insights into the behavioral and neurochemical parameters of ethanol and polydrug self- administration.